Diaphragm and associated device



Feb. 2, 1937. a MESSICK DIAPHRAGM AND ASSOCIATED DEVICE 5 Sheets-Shed 1 Original Filed March 11, 1924 NmvE Feb 2, 1937. c ss 7 2,069,551

DIAPHRAGM AND ASSOCIATED DEVICE Original Filed March 11, 1924 3 Sheets-Sheet 2 Feb. 2, 1937, c. MESSICK DIAPHRAGM AND ASSOCIATED DEVICE 3 Sheets-Sheet 5 Original Filed March 11, 1924 Patented Feb. 2, 1937 UNITED STATES PATENT OFFICE Charles Messick,

Brentwood, N. Y.

Application March 11, 1924, Serial No. 698,368 Renewed April 28, 1930 33 Claims.

This invention pertains to large diaphragms generally. It is a continuation, in part, of my applications Serial No. 383,689, filed May 24, 1920; Serial No. 427,430, filed November 30, 1920; and Serial No. 605,581, filed December 8, 1922.

A broad object of the invention is to provide an improved diaphragm for acoustical or analogous apparatus.

Other objects are to provide improved details of construction for such a diaphragm of large size, and free from troublesome natural periods, efficient, reliable, long wearing, and constant in its performance under varying weather conditions, and also capable of being combined with various well-known diaphragm auxiliaries such, for instance, as the conventional means to vary the tension of a banjo head.

Another broad object is to provide an improved compensating cushion and associated devices for use in connection with the diaphragms of receivers or projectors and transmitters or pickups.

The improved cushion is so designed as to have a tendency to oppose deflection approximately as the square of the amplitude of such deflection, thus compensating for the characteristics of the conventional electro-magnetic apparatus wherein the magnetic pull varies inversely approximately as the square of the air gap separating the armature from the pole pieces.

The improved compensating cushion co-acting with a conventional magnetic circuit thus causes vibrations in a diaphragm directly proportional to the variations in current flow instead of in proportion to the magnetic pull.

Another object of the compensating cushion and associated devices is to damp natural periods which may be present in the diaphragm and its vibratory load. This damping being a result of the characteristics of the cushion above described and also probably because in a cushion of this type. if there is a natural period at all, such natural period is above the audible range.

Another object of the detailed arrangement of the compensating cushion is to permit the spring to be surrounded by a hollow central pole piece and to thus act along the centre axis of the diaphragm.

Another broad object is to provide improved acoustical performance by combining this improved diaphragm with this improved compensating cushion and/or adjustments, etc.

Another object is to provide an improved folding protecting housing and stand for loud speakers, etc.

Each of these improvements modifies and complements the others and jointly contributes to the improved acoustical performance and efficiency in operation of my invention.

Other objects may appear from the following detail description of the preferred construction and will be pointed out in the claims.

Referring to the drawings:

Fig. 1 is a full size fragmentary plan view of the back of my improved diaphragm showing the arrangement of one of the six groups of wires, etc.

Fig. 2 is a fragmentary substantially true section, taken on the line 2-2 of Fig. 1.

Fig. 2a is a side elevation, twice full size, of one of the twin washers, showing its original bent formation before assembly with the parts, which causes the washers to flatten out, as shown in the other figures.

Figs. 3, 4, 5 and 6 are substantially true sections, twice full size, of the lacing rings and/or dampers taken respectively at said rings or dampers 3, 4, 5 and 6, of Fig. l, and looking radially toward or from the center of the diaphragm.

Fig. '7 is a view diagrammatically explaining the positions and relations of the six groups of wires, one of which appears in Fig. 1.

Fig. 8 is a half size side elevation of an improved folding loud speaker housing for my diaphragm.

Fig. 9 is a front elevation of the device of Fig. 8.

Fig. 10 is a full size substantially true sectional elevational view, taken on the line IU-l0 of Fig. 9.

Fig. 11 is a full size front elevation of the motor mechanism shown in Fig. 10.

Fig. 12 is a back view of the moulded insulation frame of the motor mechanism, shown in Figs. 10 and 11.

Fig. 13 isa back view of the iron core or yoke of Figs. 10 and 11.

Fig. 14 is a plan view of the armature of Fig. 10.

The numeral l indicates an anchorage ring or frame upon which is cemented, by means of shellac, a sheet of aluminum foil 1/ 1000 inch thick, indicated by the numeral I00. On top of the foil and fastened through it to ring I, forty-eight spring steel wires of 10/ 1000 inch diameter, tensioned approximately to the elastic limit, are provided. These wires are divided into six similar groups, numbered respectively I0, 20, 30, 40, 50 and 60, each group containing eight wires.

The wires of each group are anchored at two rows of anchor screws one row near the outer edge of ring I, and the other row near the inner edge thereof. Half the anchor screws of each row are used for anchoring the ends of wires by compressing the wires beneath twin washers, and the other half for anchorage posts upon which the wires are looped.

In Fig. '7, the positions of the outside row loop anchorages belonging to each group are indicated by narrow enclosures a, 0,, etc., and the position occupied by the end anchorages in each group are indicated by wide enclosures b, b, etc.

The loop anchorages of the inner row of each group are similarly indicated by c, 0, etc., and the end anchorages by d, d, etc.

The outside wires 3| and 38 of group 30 are also shown in Fig. 7, and all the wires SI, 32, 33, 34, 35, 36, 3! and 38 are shown in Fig. 1.

A typical wire 3|, of group 30, and its application will be described in detail, all of the fortyeight wires being similar. Wire 3| is looped around anchorage screws SIaI and 3I a2, crossed around aluminum center pin or strut I0 I, and the ends passed beneath the twin washers 3lbI and 3| b2.

A typical twin washer is shown in Fig. 2a, in its original shape before the wires are clamped beneath it. It will be noted in Fig. 201., that the washer is bent down in the middle to facilitate inserting the wires beneath it at the anchorage screws. When both anchorage screws are tightened the washer flattens out, as shown in the other figures.

Both ends of wire 3| are first subjected to a temporary tension of 2 lbs., or more even up to the elastic limit of the wire, and then clamped in place by the tightening screws 3Ib3 and 3Ib4. The tension is thus permanently fixed in that portion of wire 3| extending between the anchorages. The temporary tension is then re leased in the external end portions of wire 3i, shown in dot and dash lines at the left of Fig. l, which are then broken off. Wires numbered 32, 33, 34, 35, 36, 31 and 38, of group 30, and all the wires of groups I0, 20, 40, 50 and 60, are similarly applied to ring I.

Referring to Fig. 7, the sequence in which the wires are applied is as follows: First a wire is applied in the outside row of anchorages of group I0, then a wire correspondingly positioned in group 60, then a wire of group 20, then a wire of group 50, then a wire of group 30, for instance, wire 3|, then a wire of group 40.

The application of the above wires, one in each of the six groups, produces a symmetrical figure like a substantially flat twenty-four-spoked wheel, and owing to the sequence of the application of the wires the spokes lie nearly in the same plane where one wire crosses an adjacent wire, except for the diameter of one or two wires. This is desirable to facilitate the cementing of the aluminum foil I00 to the wires, as it is more troublesome to apply the cement properly when the adjacent wires lie in widely different planes.

After the application of the above six wires, six more wires are similarly applied at anchorage screws intermediate those to which the first six wiresare secured. After the application of the first twelve wires, twelve more are similarly applied at the intermediate anchorages. This completes the application of the twenty-four wires having anchorage near the outer edge of ring I.

A lacing ring 6, made of 10/1000 inch diameter spring steel wire is then laced between the wires above described and the ends of the lacing ring are wrapped around each other to secure the ring in position. The lacing ring 6 passes under each of the first twelve wires above described. and over each of the twelve wires last described, and is shown in Figs. 1, 2 and 6. After lacing ring 6 is completed a spacer tube I02 is slipped over center pin I0 I.

The reason for providing a row of anchorage. screws near the outer edge of ring I, and a sec-- ond row near the inner edge, is that screw heads and bodies of adequate diameter cannot be crowded in asingle row. The inner row of anchorage screws provides anchorage for twentyfour Wires, which is the same number as is provided in the outer row previously described.

Twelve additional wires are crossed over on the top of spacing tube I02 and anchored symmetrically at ring 5. These twelve wires are then laced to wires previously described by means of the lacing ring 5, shown best in Figs. 2 and 5. Thereafter the first-mentioned twenty-four wires below the spacing tube I02and the lacing ring 6 are laced to the twelve wires above the spacing tube by the lacer 6a, which consists of #30 spool cotton, and is shown in Figs. 2 and 6.

A spacing tube I03 is then slipped over pin IIlI until it rests on the'twelve wires last applied and twelve more wires are applied on top of tube M3.

The last applied twelve wires are laced to the thirty-six wires previously applied by lacing ring 3, as best shown in Fig. 3, and by cotton lacers 4, 5a and 61), best shown in Figs. 4, 5 and 6, respectively. The principal object of the lacing rings and lacers is so to truss the whole area of the diaphragm that it will tend to move in synchronism with pin I 0|.

By shortening or lengthening the unlaced lengths of wires at the flat areas of the diaphragm and varying the relative proportions of the parts, any troublesome natural periods of the diaphragm can be corrected. The diaphragm of the preferred construction is designedwith the flat portions, each having a different'length of supporting wire between the concentric lacing rings or lacers.

After the parts are assembled, the aluminum foil I00 is cemented to the adjacent portions of all the wires. The wires thus act like the masts of a ship and the foil like the sails.

The attachment between the forty-eight wires and the aluminum foil I00, may be conveniently effected by inverting the diaphragm from the position of Fig. 2, rubbing the foil with a felt pad to make the foil hug the wires and again inverting the diaphragm back into the position of Fig. 2.

A thin coat of lacquer may then be flowed over the foil until it and the adjacent portions of the wires are fully coated. The diaphragm may then be again inverted from the position of Fig. 2 and quickly dried over artificial heat while it is being rubbed with a felt pad to press the foil and the adjacent wires into contact.

Or, with the diaphragm in the position of Fig. 2 an upward air pressure may be applied to the foil, and lacquer applied by means of an air brush, to effect the cementing.

Referring to Figs. 1 and 7, it will be noted that holeslii i, I04, etc. are provided between each group of wires. These holes are designed to re ceive through screws for mounting the ring I in a loud speaker, or elsewhere, as desired.

Referring to Fig. 1, it will be noted that the anchorage screws are so arranged that the distance between each wire and its nearest neighbor are equal. This symmetry tends to reduce the unsupported area of the foil I00 between the wires 3I, 32, etc.

After the diaphragm is formed, as above described, a radially furrowed appearance may be seen looking down upon it, as in Fig. 1. This is due to the use of the felt pad, causing the foil I00 to hug the wires.

In Fig. 2, the rim of a banjo is indicated at I I0 in dot and dash lines, over which the diaphragm as a whole may be tightened in the conventional way, if desired, but owing to the stability of the tension of the spring steel wires in my diaphragm, such a tension device is ordinarily superfluous.

In Fig. 2 is also indicated at I20, in dot and dash lines, a fragment of a protective shell, which may be fitted on the back of the diaphragm to protect it from accidental injury. At the front of the diaphragm is also indicated a fragment of the protective grill I30, to protect the front of the diaphragm, and also if desired to support a vibratory motor or generator unit for connection to the diaphragm.

I have observed that the natural period of a wire exceeding about one and one-half inches in undamped length is audible in this diaphragm. Such length therefore is not exceeded in the diaphragm above described.

All of the factors within ring I may be varied experimentally in size, proportion, tension, and number when repeated observation makes noticeable a natural period or other defect in performance of the diaphragm. Defects attributable to the motor mechanism, etc. must, however, be corrected before much further refinement of the diaphragm is possible. When a more perfect motor is available, further refinement of the diaphragm can probably be made by varying the factors.

Referring to Fig. 8 and Fig. 9, my loud speaker is shown, including the assembly of ring I in a protecting shell I20 and grill I30. The grill I30 is provided with a vibratory electro-magnetic motor or generator 200 at its central portion, and with a leg casting I3I, provided with two legs I32 and I33, and fastened to the grill, etc. by screws, as indicated.

The legs I32 and I33 are provided with a folding back leg I34 which folds against the grill I30, as indicated in dot and dash lines, for compactness of packing. In the indicated position, legs I32, I33 and I34 form a stable tripod for the support of my loud speaker.

Shell I20 may be perforated if desired, in order to permit free air to have access to the back of the diaphragm, that is, the surface of the diaphragm remote from grill I30.

Referring to Fig. 10, the diaphragm is indicated diagrammatically at I0, provided with the ring I, the perforated protecting shell I20, the grill I30, and the leg casting I3I. At the left, a machine screw and nut Ia, secures grill I30, ring I and shell I20 together, and at the right a longer machine screw lb, secures the leg casting I3I, the grill I30, the ring I, and the shell I20 together.

It should be noted that ring I is provided with a shoulder Ic to center shell I20 and that grill I30 is provided with a shoulder I30a, to center the grill with the ring I.

I have tried several motor units of conventional type for the operation of my diaphragm above described and have found each type so far tried to exhibit one or more troublesome natural periods. I have therefore designed a special motor unit which I believe will combine with my diaphragm to give superior results. However, I have no reason to think that this improved motor unit would fail to also improve the performance of conventional diaphragms.

The vibratory motor or generator 200 includes a frame of moulded insulation 20I of the shape indicated in Figs. 10, 11, and 12. Frame 20I is attached to grill I30 by machine screws 202, 203 and 204.

A soft iron core 2), which is best shown in Figs. 10 and 13, is provided with an external thread 2 I I, which mates with an internal thread 2I2 in the moulded insulation 20I. The threads are shellacked and screwed together, so that when the shellac hardens these parts become permanently attached to each other.

Core 2I0 is provided with a conventional winding 220 on a spool 22I, which is held in place by the friction washer 222.

The upper face, according to Fig. 10, of core 290 is ground fiat and a flexible armature 2I3 laid upon it. This armature 2I3 is loosely held in place by the cap 2M which screws onto the upper end of the external thread 2H of core 2I0.

Through a slot 2I5, designed to prevent inductive losses in core 2H1, leads 223 and 224 from winding 220, lead through moulded insulation 20I, as indicated in Figs. 10 and 12, to binding posts 225 and 226, respectively. These binding posts 225 and 226 are both mounted on moulded insulation 20I and may be suitably connected by a flexible cord 228, so that the motor will operate as a receiver or transmitter.

The center of core 2I0 is bored and threaded with a buttress thread 230, which engages a threaded plug 23I, in such a manner that when the plug is pressed downward according to Fig. 10, considerable friction will be developed at the thread and it will not tend to revolve and get out of adjustment when subjected to vibration. Plug 23I is provided with an adjustable knurled nut 232. which may be locked on the plug by means of the set screw 233.

At the upper end of plug 23I. a flat cone pointed cushion 240 is tightly inserted i th recess of plug 23I. Cushion 240 may be preferably made of steel wool compressed to the form shown, or cork, felt. rubber, leather like a billiard one tip, or such elastic material as the associated apparatus with which it is to operate requires. The exact form of cushion 240 is like the sounding board of a piano, rather the product of an expert workman than the result of exact predetermined design.

Cushion 240 is intended to perform in an improved manner the function ordinarily performed by the elasticity in the conventional soft iron diaphragm to retract the diaphragm from the pole pieces. In my case, it serves to retract armature 2I3 from hollow cylindrical pole piece ZIES of core 2I0.

The air gap between pole piece 2I6 and armature 2I3 may be varied by adjusting plug 23! by knurled nut 232. But the knurled nut 232 should be locked on plug 23! in a position to abut core 2") when the maximum required air gap is attained, so as to prevent the excessive bendin of armature 2| 3.

Cushion 240 is intended to resist compression approximately as the square of the distance compressed and thus compensate for the variation of the magnetic pull, which approximately varies inversely as the square of the air gap. The conventional soft iron diaphragm, 0n the other hand, resists deflection according to Hoo'ks law, or approximately so.

This improved cushion 240 also appears to have a tendency to damp natural periods in the whole vibratory system. The causes of this dampening tendency are probably the very high natural period of the cushion material under compression and cone point of the cushion. In the cone point, the cross section under compression varies as the armature 213 vibrates.

Armature M3 is permanently adjusted in driving contact with pin Hll and thus vibrates the diaphragm 29! when the apparatus is used as a loud speaker, or is vibrated thereby, when the apparatus is used as a pickup. The adjustment of this driving contact may be effected by lengthening or shortening pin I JI, or by inserting shims between grill I30 and moulded insulation 21H at the abutting portions.

The expression concave cone wherever used is intended to mean a formation projecting from the plane of a base which decreases in steepness from the apex toward the base.

I claim:

1. A diaphragm including a stationary frame, highly tensioned vibratory wires anchored at the frame and a sheet of metal attached to the wires Where adjacent thereto.

2. An acoustical diaphragm including the combination of a stationary anchorage frame, a vibratory skeleton framework anchored at the frame, and a relatively flexible sheet metal covering mounted upon the framework whereby the diaphragm is rendered imperforate to air.

3. An acoustical diaphragm including the combination of a stationary anchorage frame, a highly tensioned vibratory skeleton framework anchored at the frame, and a sheet metal covering mounted upon the framework whereby the diaphragm is rendered imperforate to air.

4. The combination in an acoustical diaphragm of a rigid frame, a vibratory member mounted therein and including a vibratory framework and a relatively flexible sheet metal member imperforate to air, said vibratory member being tensioned at the rigid frame.

5. The combination of a rigid anchorage frame and a tensioned vibratory member within the frame provided with a central strut and means intermediate the strut and the frame to draw the two external portions of the member together into one plane, a second means intermediate the strut and the first means to deflect the adjacent portions of the member into the general form of a double concave cone with the strut as the apex, whereby the vibratory member may vibrate in phase with any vibratory force applied thereto.

6. A diaphragm provided with a stationary peripheral anchorage frame, a vibratory means therein having a flat outer edge portion and including two members under radial tension and anchored to the frame, means to space the members. apart at the centre and means to space the members a predetermined distance from each other intermediate the centre and edge portion.

7. A diaphragm provided with a peripheral anchorage frame, a vibratory means having a flat outer portion, including three members under radial tension to the frame, a compression member at the centre to space the three members apart; means to hold two of the three members in the one plane a distance from the centre and means at a greater distance from the centre to hold all three members together in the plane of the flat portion.

8. A diaphragm provided with a peripheral anchorage frame, a tensioned vibratory means therein having a fiat outer portion adjoining the frame, a shallow conical portion within the flat portion and a steeper conical portion within the shallow conical portion.

9. A diaphragm including a stationary frame, tensioned vibratory wires the ends whereof are anchored at the frame in one general plane, said wires being divided at the centre of the diaphragm into at least two groups spaced apart by a compression member and secured together in said plane by a means between the compression member and the anchorage and a second means between the compression member and the first means to deflect the wires of the two groups toward each other.

10. The combination of an anchorage frame, a vibratory diaphragm within and tensioned to the frame, and a strut at the central portion of the diaphragm having more than two shoulders for holding several portions of the diaphragm away from the general plane thereof at different levels, and portions of the diaphragm held at each of said levels.

11. The combination of a frame, a vibratory diaphragm therein including means capable of sustaining tension and imperforate to air, radially tensioned and attached at its outer edge to an anchorage portion of the frame, and central means to deflect the first mentioned means out of the plane of the anchorage portion into substantially the shape of a concave cone including most of the area of the diaphragm and assuming an increasingly flat form as the anchorage portion is approached.

12. A sound reproducer of the character described, comprising, in combination, a supporting frame, a Vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing vibrations to said membrane.

13. A sound reproducer of the character described, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing vibrations to said membrane, said resilient means including a vibatory member to which said membrane is connected.

14. A sound reproducer of the character described, comprising, in combination, a supporting frame, a vibratory membrane mounted in association with said frame, resilient means maintaining said. membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing vibrations to' said membrane, said resilient means being adjustable whereby the tension on the membrane may be varied.

15. The combination of a frame, an acoustical diaphragm therein including a surface extending at its outer edge to the frame, provided with a larger amount of material per unit area at a central portion, and yielding means to deflect said portion into substantially the shape of a concave cone.

16. The combination in an acoustical diaphragm of a peripheral stretching frame, a vibratory portion within the frame, said vibratory portion being provided with radiating wires attached at the frame, and a membrane supported by said wires.

17. The combination of a frame provided with a hole, a. tensioned member covering the hole, provide-d with a projecting central portion, a flatter portion surrounding said projecting portion, and tensioned metallic means anchored at the frame in intimate contact with and supporting the flatter portion of said membrane.

18. The combination of a frame provided with a hole, a tensioned membrane covering the hole, provided with a projecting central portion, and a flatter portion near the frame, tensioned supporting means for said flatter portion and anchorage members for said means passing through the edge of said membrane and into said frame.

19. A device as in claim 12 wherein the membrane is of metal, whereby it is substantially free from expansion and contraction due to changes in atmospheric humidity.

20. In combination, a flexible membrane diaphragm, a support for the periphery of said diaphragm, means for tensioning said diaphragm and for fastening said diaphragm to said support and driving means for said diaphragm positioned to engage a portion thereof which is not in the plane through the peripheral portion of the diaphragm, the peripheral portion of said diaphragm having substantially a plane surface and the central portion of said diaphragm having substantially the shape of a cone.

21. The combination of a frame, a tensioned diaphragm of loud speaking area, substantially in the shape of a concave cone, an electric motor provided with an armature in driving relation to the diaphragm, substantially at the apex of the cone and elastic means to stress the diaphragm through the armature.

22. A sound reproducer of loud speaking area and of the character described, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane being strengthened around said point, whereby the material of which it is made will be more effectively disposed to resist said resilient means, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing vibrations to said membrane.

23. A device as in claim 22 in which there are several separate means for strengthening the membrane at the point, which extends radially therefrom.

24. An acoustical diaphragm comprising, in combination, a stationary peripheral frame, a vibratory portion within the frame, having a stiff, substantially concave conical portion and a relatively flexible edge, said conical portion including means to substantially define the shape of the central portion of said conical portion and a surface means covering said defining means and designed to cooperate and move as a unit therewith.

25. An acoustical diaphragm comprising in combination, a stationary peripheral frame, a vibratory portion within the frame and radially tensioned thereto, having a stiff substantially concave conical portion and a relatively flexible edge, said conical portion including means to substantially define the shape of the central portion of said conical portion and a surface means covering said defining means and designed to cooperate and move as a unit therewith.

26. An acoustical diaphragm comprising in combination, a stationary peripheral frame, a vibratory portion within the frame and radially tensioned thereto, having a stiff, substantially concave conical portion and a relatively flexible edge, said conical portion including means containing more material per unit area to substantially define the shape of the central portion of said conical portion and a surface means covering said defining means and designed to cooperate and move as a unit therewith.

27. A loud speaker provided with a diaphragm of direct acting area, having a substantially conical central portion and a stationary motor mounted substantially in line with the axis of the conical portion, said motor being provided with a movable actuating and damping means in actuating and damping relation to said conical portion, whereby excessive movement of the dia phragm, at resonance, is appreciably damped.

28. A device as in claim 15 in which the larger amount of material per unit area at the central portion consists of close together radial means, separated from each other at a distance from the central portion.

29. The combination of a frame, a vibratory diaphragm of direct acting area therein, extending from a centre and tensioned to said frame, concentric sections of said diaphragm being of greater average thickness near the centre than remote therefrom, said diaphragm including many tension means radiating from the centre and separated from each other where remote therefrom, and elastic means to deflect the diaphragm into substantially the shape of a concave cone.

30. A diaphragm including the combination of a stationary peripheral frame, a first means, substantially imperforate to air, of loud speaking area and enclose-d in the frame, deflecting means connected to the first means whereby it is tensioned substantially into the shape of a concave cone, gradually increasing in steepness toward the centre, said first means being so designed that the apex of the cone contains more material under tension per unit area than the outer portion thereof, whereby vibrations applied at the apex may be effectively distributed.

31. The combination of a stationary peripheral frame, a diaphragm within the frame in the general form of a cone of increasing steepness as its centre is approached, actuation attachment means at the apex of the cone and adjustable tensioning means for the edge portion of the diaphragm.

32. The combination of a frame, an acoustical diaphragm therein of large and direct acting area, including a surface extending at its outer edge to the frame, yielding means to deflect a central portion thereof into substantially the shape of a concave cone having a steeper apex than edge portions; said diaphragm being pro- CHARLES lvrnssrcx. 

